The present invention relates to seismic acquisition in general and, in particular, to methods and systems for conducting reconnaissance marine seismic surveys.
Petrochemical products such as oil and gas are ubiquitous in society and can be found in everything from gasoline to children's toys. Because of this, the demand for oil and gas remains high. In order to meet this high demand, it is important to locate oil and gas reserves in the Earth. Scientists and engineers conduct “surveys” utilizing, among other things, seismic and other wave exploration techniques to find oil and gas reservoirs within the Earth. These seismic exploration techniques often include controlling the emission of seismic energy into the Earth with a seismic source of energy (e.g., dynamite, air guns, vibrators, etc.), and monitoring the Earth's response to the seismic source with one or more receivers in order to create an image of the subsurface of the Earth.
Conventional marine seismic surveys generally involve towing one or more streamer cables with a plurality of receivers behind an acquisition vessel. Each receiver includes, for example, a pressure sensor and/or a particle motion sensor in proximity to one another. The pressure sensor may be, for example, a hydrophone that records scalar pressure measurements of a seismic wavefield. The particle motion sensor may be, for example, a three-component geophone that records vectorial velocity measurements of the seismic wavefield. By observing the reflected seismic wavefield detected by the receiver(s) during the survey, the geophysical data pertaining to reflected signals may be acquired and these signals may be used to form an image indicating the composition of the Earth near the survey location.
It can be very expensive to acquire and process the data collected in towed-streamer marine seismic surveys. The acquisition can be expensive because of the large amount of equipment and coordination required to plan and carry out a towed-streamer survey. Conventional 3D towed-streamer acquisition geometries typically include 5-15 streamers towed, together with one or more sources, behind an acquisition vessel, with the streamers spaced at 50-100 meters and towed at a depth of about 10 meters. The vessels usually tow the streamers in a “racetrack” geometry, with swaths defined by the streamers overlapping by 50% or more in successive acquisition lines. In many cases, the reason for such large overlap is because of the relatively sparse coverage in the near offset range (i.e., for the receivers closest to the vessel and source) that needs to be infilled in subsequent acquisition lines.